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Add indicative QP for ASP and AVC codecs

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git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@17057 b3059339-0415-0410-9bf9-f77b7e298cf2
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gpoirier 2005-11-27 19:48:39 +00:00
parent 70d1fd2150
commit f5373be10e
1 changed files with 21 additions and 3 deletions
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24
DOCS/xml/en/encoding-guide.xml
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@ -1043,6 +1043,9 @@
<sect3 id="menc-feat-dvd-mpeg4-resolution-bitrate-compute">
<title>Computing the resolution</title>
<para>
The following steps will guide you to compute the resolution of your
encode without taking too much distortion by taking into account several
information about the souce video.
First, you should compute the encoded aspect ratio:
<systemitem>ARc = (Wc x (ARa / PRdvd )) / Hc</systemitem>
<itemizedlist>
@ -1079,17 +1082,30 @@
</para>
<para>
The CQ depends both on the bitrate and the movie resolution.
The CQ depends both on the bitrate, the video codec efficiency and the
movie resolution.
In order to raise the CQ, typically you would downscale the movie given that the
bitrate is computed in function of the target size and the length of the
movie, which are constant.
A CQ below 0.18 usually ends up in a very blocky picture, because there
With MPEG-4 ASP codecs such as <systemitem class="library">XviD</systemitem>
and <systemitem class="library">libavcodec</systemitem>, a CQ below 0.18
usually ends up in a pretty blocky picture, because there
are not enough bits to code the information of each macroblock (MPEG4, like
many other codecs, groups pixels by blocks of several pixels to compress the
image; if there are not enough bits, the edges of those blocks are
visible).
It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip,
and 0.26-0.28 for 2 CDs.
and 0.26-0.28 for 2 CDs with standard encoding options.
More advanced encoding options such as those listed here for
<link linkend="menc-feat-mpeg4-lavc-example-settings"><systemitem class="library">libavcodec</systemitem></link>
and
<link linkend="menc-feat-xvid-example-settings"><systemitem class="library">XviD</systemitem></link>
should make it possible to get the same quality with CQ ranging from
0.18 to 0.20 for 1 CD rip, and 0.24-0.26 for 2 CDs
With MPEG-4 ASP codecs such as <systemitem class="library">x264</systemitem>,
you can use a CQ ranging from 0.14 to 0.16 with standard encoding options,
and should be able to go as low as 0.10 to 0.12 with
<link linkend="menc-feat-x264-example-settings"><systemitem class="library">x264</systemitem>'s advanced encoding settings</link>.
</para>
<para>
@ -1098,6 +1114,8 @@
to a movie such as The Matrix, which contains many high-motion scenes.
On the other hand, it is worthless to raise CQ higher than 0.30 as you would
be wasting bits without any noticeable quality gain.
Also note that as said earlier on this quide, low resolution comparatively
need a bigger QP to look good.
</para>
</sect3>